Proportional escapement apparatus for a single element typewriter



Oct. 10, 1967 W.,O.-CRALLE, JR.. ETAL 3,346,086

- PROPQRTIONAL ESCAPEMENT APPARATUS FOR A SINGLE v ELEMENT TYPEWRITER Filed Sept. 25, 1963 Y 6 She ets-Sheet 1 INVENTORS. WALTER 0. CRALLE GEORGE A. HOLT EDWIN J4 LENNEY DOUGLAS E. SEDERHOLM NEIL D. WALTON ATTORNEY.

CRALLE, JR. ETAL PEMENT APPARATUS FOR A $1 ELEMENT TYPEWRITER 3,346,086 NGLE Oct. 10, 1967 w. 0.

PROPQRTIONAL E50 6 Sheets-Shet 2 A 6 Filed Sept. 25, 1963 FIG. 2

. r I 4 n m a 1 p u k a as. a 7. v 1

Oct. 10, 1967 w. o. CRALLE, JR; ET AL- 3,346,036 PROPORTIONAL ESCAPEMENT' APPARATUS FOR- A SINGLE ELEMENT TYPEWRITER v Filed Sept. 25, 1963 6 Sheets-Sheet 5 FIG. 5

Oct. 10, 1967 w A PROPORTIONAL ESGAPEMENT APPARATUS FOR A SINGLE I I ELEMENT TYPEWRITER Filed Sept. 25. 1963 CRALLE. JR, ETAL 3,346,086,.

Oct. 10, 196

PROPORTIONAL ESCAPEMENT APPARATUS FOR A SINGLE ELEMENT TYPEWRITER Filed Sept. 25', 1963 7 W.C..CRALLE,JR.. ETAL 3,346,086

6Sheets-Sheet 5 v v w. o. CRALLE, JR.. ETAL 3,346,086

APEMENT APPARATUS FOR A SINGLE v v Oct. 10, 1967 PROPORTIONAL ESC ELEMENT TYPEWRITER '6' Sheets-Sheet 6 FiIeds t. 25, 1953 United States Patent 3,346,086 PROPORTIONAL ESCAPEMENT APPARATUS FOR A SINGLE ELEMENT TYPEWRITER Walter (lrCralle, Jr., George A. Holt, Edwin J. Lenney, Douglas E. Sederholm, and Neil D. WaltomLexington, Ky., assignors to International Business Machines Corporation, New York, N.Y., a corporation of New York Filed Sept. 25, 1963, Ser. No. 311,373 28 Claims. (Cl. 197-84) The present invention relates generally'to the typewriter and printing arts and more particularly to the provision of proportional escapement apparatus and associated mechanism for use in a typewriter having a single replaceable print element. The print element is moved in a character spacing direction with respect to a stationary printing platen under the control of the proportional escapement apparatus.

A single element typewriter where the print element moves with respect to a stationary printing platen otfers many and significant advantages with respect to more conventional typewriters. The print element is easily removed and replaced so that the type style or font is readily change-d. The mass and bulk of the movable carrier mounting the print element and associated apparatus are substantially reduced when compared with the mass and bulk of the conventional movable printing platen. This permits smaller and less complicated parts to be employed while yet providing a highly reliable typewriter. A single element typewriter of the above type is manufactured by International Business Machines Corporation, Armonk, N.Y., and is sold under the trademark Selectric. A complete description of this typewriter is set forth in the IBM Customer Engineering Series 72 Instruction Manual, Form 241-5032-0, copyright 1961.

Briefly, the present invention is concerned with the provision of proportional escapement apparatus for a single element typewriter whereby the interchangeable print element is moved through various escapement distances in accordance with the characters selected by the typist. The proportional escapement apparatus comprises a plurality of settable elements, such as pins, arranged in a closed pat-h. Each of the settable elements represents a single basic escapement unit and is settable to either of two states or conditions. Setting and escapement assemblies are located adjacent the path of travel of the settable elements. Character escapement selection apparatus controls the setting assembly to regulate the states of the settable elements in response to character selection by the typist. The escapement assembly is responsive to the states of the settable elements as regulated by the setting assembly and limits relative movement between the settable elements and the escapement assembly to determine the number of basic escapement units associated with an escapement operation.

Backsp acing apparatus is provided to permit backspacing on a character-bycharacter basis. In essence, the settable elements define a limited memory which stores information corresponding to past escapement operations. The backspacing apparatus comprises sensing apparatus and means for etfecting reverse relative movement between the escapement assembly so that a typist can backspace on a character-by-ch araoter basis to move the print element to a previous printing position. Forward spacing apparatus is also provided whereby after backspacing on a character-by-chanacter basis to a previous printing position, the print element can be advanced to the last or furthest printing position on a character-by-character basis. The above is a particularly important feature of the present invention since the complicated and time consuming visual alignment operations required in performing backspacing and/or forwardspacing operations with 3,345,086 Patented Oct. 10, 1967 prior art proportional escapement typewriters are completely eliminated.

The carrier mounting the interchangeable print element is drivingly connected to a lead screw which extends in generally parallel relation with respect to the stationary printing platen and this lead screw is biased for rotation in one direction by a constant torque device. The amount of movement imparted to the lead screw during each escapement operation is controlled by the states of the settable elements and the setting of adjustable gearing means. The adjustable gearing means is positioned in driving relation between the lead screw and the escapement apparatus to provide the typist with a means for changing or varying the incremental distance moved by the print element for each basic escapement unit corresponding to one of the settable elements.

It is the primary or ultimate object of the present invention to provide proportional escapement apparatus of a type particularly adapted for use with a single element typewriter. In particular, this escapement apparatus comprises a pin wheel carrying a plurality of settable pins which, in combination with adjustable gearing means, is adapted to limit the rotary movement imparted to a lead screw by a constant torque device. The lead screw has a driving connection with the carrier mounting the single print element.

Another object of the present invention is to provide improved apparatus for moving the pins on the pin wheel to the desired states in response to character selection by the typist. The pin setting assembly comprises a plurality of pin setting arms and interposers which are interconnected to provide a highly compact mechanical assembly adapted to regulate the states of a plurality of the pins at the same time. As will be hereinafter more fully apparent, some of the pins are always maintained in or moved to predetermined state-s while others of the pins are maintained in or moved to either of their states depending upon the relative size or width of the character selected by the typist.

Yet another and highly important object of the invention is the provision of a proportional spacing typewriter having memory or storage capability for past escapement information. This permits the typist to backspace to a previous printing position for correcting mistakes or the like in an improved and simplified manner. The typist is not required to visually align the position of the carrier as is necessary in prior art proportional escapement typewriters. In addition, means are provided to permit forwardspacing on a character-by-character basis from a previous printing position to the last or furtherest printing position.

A further object of the invention is to provide a typewriter having the characteristics described above which is extremely versatile but yet is simple to operate and can be manufactured at a relatively low cost. The typewriter is adapted to produce printed text in any of a wide variety of type styles and can perform printing operations usually associated with expensive and complicated printing and composing apparatus.

The foregoing and other objects and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention as illustrated in the accompanying drawings.

In the drawings:

FIGURE 1 is a front perspective view of a single element typewriter embodying proportional escapement apparatus constructed in accordance with the teachings of the present invention;

FIGURE 2 is a side perspective view of a portion of the apparatus shown in FIGURE 1 and illustrating in greater detail the escapment control apparatus including the pin wheel, the escapement assembly and the pin setting assembly;

FIGURES 3 and 4 are plan sectional views taken along the section lines 33 and 4-4, respectively of FIG- URE 2;

FIGURE 5 is a view similar to FIGURE 2 showing the backspacing apparatus associated with the pin wheel;

FIG. 6 is a side elevational view depicting a portion of the backspacing apparatus and particularly the mechanism for imparting reverse driving movement to the pin wheel;

FIGURE 7 is a side perspective view of a portion of the backspacing apparatus including the means for sensing the presence of a set pin;

FIGURE 8 is a front perspective view showing in detail the construction of the pitch changing apparatus;

FIGURE 9 is a sectional view taken generally along the section line 99 of FIGURE 8;

FIGURE 10 is an enlarged plan view of the character storage indicator employed with the typewriter of FIG- URE 1;

FIGURE 11 is a sectional view showing details of the changeable scale means and the character storage indicator taken along the section lines 1111 of FIG- URE 10; and

FIGURE 12 is a sectional view depicting the constant torque device used in the typewriter taken along the section line 12-12 of FIGURE 1.

Referring now to the drawings, and initially to FIG- URE 1 thereof, the reference numeral 10 designates generally a single element typewriter with proportional escapement apparatus constructed in accordance with the teachings of the present invention. The typewriter comprises an interchangeable print element 11 detachably secured to a mounting post 12. The print element 11 is mounted from a rocker plate 13 which in turn is pivoted by pins 14 to a carrier 15. The carrier is mounted for longitudinal sliding movement on guide shaft 16 in front of a stationary printing platen 17. The carrier has a connection, not particularly shown, with an elongated lead screw 18 extending in generally parallel relation with respect to the printing platen 17. The distance and direction of the angular rotations imparted to lead screw 18 determine the extent and direction of the escapement and backspace movements of the single print element 11.

The print element 11 has the general shape of a truncated spheroid and a plurality of different size characters 20 formed thereon are arranged in generally aligned horizontal and vertical rows. The typewriter is provided with a plurality of character keylevers, such as keylever 21, and a number of function keylevers, including a case shift keylever, not shown. Each of the character keylevers is associated with two of the characters formed on the print element with the state of the case shift keylever determining which of the two characters is selected. For example, if only the keylever 21 is depressed, the lower case h is selected; while if both the keylever 21 and the case shift keylever are actuated, the upper case or capital H is selected. The print element 11 is mounted for rotational and tilting movements on the rocker plate 13 and these movements are controlled by character selection apparatus, not shown, in response to keylever actuation to bring a selected character into printing posi tion.

After the print element has been rotated and tilted as required to bring a selected character into printing position, the rocker plate 13 mounting the print element is pivoted upwardly about pins 14 by the action of print cam 23 which is slidably mounted on guide shaft 16 for longitudinal movement with carrier 15. The guide shaft is rotated during each print cycle by an electric motor operating through suitable clutch and driving apparatus, not shown, to cause the print element to be rocked forward toward the printing platen 17 and effect printing of the selected character. The print element falls back from the printing platen and is returned to its original or home position. The lead screw 18 is then rotated and the print element advances by an escapement distance corresponding to the size or width of the previously selected and printed character.

In general, a character printing operation is characterized by three major steps. The first step is the selection of a character and the rotation and tilting of the print element as required to bring the selected character into printing position; the second step comprises rocking the print element toward the printing platen to effect printing of the character; and the third step includes advancing the print element by a distance proportional to the size or width of the printed character. This invention is primarily concerned with apparatus for accomplishing the third step and to avoid unnecessary complexity in the present application, only the apparatus directly associated with the escapement of the print element (the third step) is shown and described in detail. However, the character selection and printing apparatus is primarily the same as that employed in the IBM Selectric typewriter and those desiring a more detailed explanation thereof should refer to the above identified instruction manual. I

The escapement apparatus for the typewriter comprises the lead screw 18 and means for rotating the lead screw in the proper direction and through a preselected angular distance corresponding to escapement distance associated with a selected character. During printing or forwardspacing operations, the carrier 15 and print element 11 are moved on a character-by-character basis from left to right in front of the printing platen 17 when looking at FIGURE 1 of the drawings. When backspacing is accomplished, the print element moves in the opposite direction on a c'har-acter-by-character basis. In general, the escapement apparatus comprises a constant torque device 25 and associated driving means which rotate the lead screw 18 and permit the carrier 15 and print element 11 to advance with respect to the printing platen 17; escapement control apparatus 26 having a plurality of settable elements defining a limited memory; character escapement selection apparatus 27 for controlling the states of the settable elements in response to the characters selected; and pitch changing apparatus 28 providing a variable drive connection between the escapement control apparatus 26 and the lea-d screw 18 for changing the pitch of the printing. The escapement control apparatus 26 is actuate-d by the character escapement selection apparatus 27 in response to character or function selection by the typist to control, in combination with the pitch changing apparatus 28, the angular movement imparted to the lead screw by the constant torque device 25. During backspacing operations, the escapement control apparatus 26 is itself driven to drive the lead screw 18 via the pitch changing apparatus 28.

To facilitate the description and understanding of the present invention, the constant torque device 25, escapement control apparatus 26, character escapement selection control apparatus 27 and pitch changing apparatus 28, along with other ancillary mechanisms, will be described in detail under separate topic headings below with the overall operation and co-action of the various instrumentalities set forth at the end of the specification.

Escapement control apparatus In the typewriter and printing arts, it is well known to group or divide the characters of a character set into various groups and assign a different number of basic escapement units to each such escapement group. For example, the smaller characters, such as i, 1, period and the like may be assigned two units of escapement; the intermediate size characters, such as a and n, three units of escapement; and the larger size characters, such as m and w, four units of escapement. This grouping of the characters is employed in the illustrated embodiment of the present invention. However, it should be clearly understood at the outset that this particular grouping is meant to be illustrative only since more or les than three basic character size groups can be employed. As will be hereinafter more fully apparent, one of the primary advantages of the present invention is that the escapement control apparatus 26 in combination with the pitch changing apparatus 28, can be designed to operate for almost any selected escapement scheme with a minimum of design change.

Refering now to FIGURES 24 of the drawings, the escapement control apparatus 26 is, shown to comprise a pin wheel 30 keyed to shaft 31. The shaft 31 is journalled for rotation in a generally U-shaped mounting bracket 32 which is located in the right rear portion of the typewriter. The pin wheel 30 has a plurality of axially extending and equally circumferentially spaced slots 33 and a circumferentially extending recess 34 of semi-circular cross section formed about the periphery thereof. Received in each of the slots 33 is a pin 35 whose length is longer than the thickness of the pin wheel 30 so that one end portion thereof projects axially outward from the slot. Each pin 35 has a pair of semi-circular recesses 36 and 37 in the upper edge thereof as is most clearly shown in FIGURE 3 of the drawings. Received in the semicircular recess 34 and extending about the pin wheel 30 is a garter spring 38. The garter spring 38 and the recesses 36 and 37 in the pins 35 define a detent means for maintaining each of the pins in one of two states. The first or set state for a pin 35 is when the spring 38 is received in recess 37 and the end portion of the pin projects outwardly from the slot 33 on the left side of the pin wheel as shown in FIGURE 3 of the drawings. A pin is in its other or reset state when spring 38 engages recess 36- and an end portion of the pin extends outwardly from the other or right side of the pin wheel. The pin wheel 30 and its associated pins 35 define a memory having a plurality of memory elements capable of assuming either of two states. The distance between any two of the pins 35 defines a standard or basic single escapement unit.

The shaft 31 mounting the pin wheel 30 is operatively connected via suitable gearing and the pitch changing apparatus 28 to the lead screw 18. The constant torque device 25 exerts a force on the lead screw which tends to rotate the same in a clockwise direction and, as a consequence, the pin wheel 30 is biased for rotation in the direction indicated by the arrows 39. In addition to the pin Wheel 30 itself, the escapement control apparatus 26 com prises an escapement pawl assembly 40, a pin setting assembly 41 and backspacing apparatus to be later described.

The escapement pawl assembly 40' comprises an escape ment pawl 43 having an elongated slot 44 therein which serves to mount the pawl for pivotal and limited longitudinal movement on pin 45. The escapement pawl 43 is positioned to one side of the pin wheel 30 in such a manner that the tip portion 46- of the pawl is adapted to engage only the ends of the set pins 35 which project outwardly from the pin wheel and does not engage any of the pins 7 that are in the reset condition. The tip portion 46 of the pawl is normally biased into engagement with the set pins by a tension spring 47. An escapement pawl trip lever 48 is pivoted on the pin 45 and has an end portion which overlies the rear end of the escapement pawl 43. Escapement pawl trip lever 48 is momentarily rocked in a counterclockwise direction by a force applied to pull link 49 each time an escapement operation takes place. Rotation of the escapement pawl trip lever 48 pivots the tip portion 46 of the escapement pawl 43 out of engagement with the set pins 35 and the pin wheel 30 is free to rotate under the action of constant torque device 25. As soon as the escapement pawl 43 is released, this member slides forwardly on pivot pin 45 due to elongated slot 44 and the action of spring 47. The rear end of the escape ment pawl 43 moves from beneath the escapement pawl trip lever 48 and the spring 47 pivots the pawl tip portion 46 back into engagement with the set pins. The next pin 35 which is in the set state engages the tip of the escapement pawl 43 and moves the pawl rearwardly until the forward edge of the elongated slot 44 in the pawl abuts against pin 45. This stops the rotation of the pin wheel 30 and defines the end of a forward escapement movement for carrier 15 and print element 11. The distance between the set pin engaged by the escapement pawl and the next adjacent set pin in the direction of rotation of the pin wheel is the extent of angular movement of the pin wheel during the next escapement operation.

Also mounted for pivoting movement on pin 45 in aligned side-by-side relation with respect to the escapement pawl 43 is a holding pawl 50 having a tip portion a 51 which is normally biased for engagement with the pins 35 by spring 47'. The holding pawl is positioned so the tip portion thereof may engage each one of the pins 35 regardless of the state thereof. This is accomplished by providing a slot 52 along one side of the pin Wheel and it should be noted that a portion of each pin is always Within this slot. The holding pawl 50 is necessary for backspacing operations since theescapement pawl 43 is not adapted to engage each of the pins. During a forward escapement movement, the end portion of the escapement pawl trip lever 48 first engages the rear end of the holding pawl 50 and lifts the tip portion 51 thereof from engagement with the set pin 35. The pin wheel 30 is held at this time since the tip portion of the escapement pawl 43 still engages the set pin 35. Eventually, and after the holding pawl has been removed from engagement with the pins, the end portion of escapement pawl trip lever 48- bears against the rear end of escapement pawl 43. The escapement and holding pawls then pivot in a counterclockwise direction as a unit and the tip 46 of the escapement 43 is removed from engagement with the set pin 35. The spring 47 immediately moves the escapement pawl 43 forward due to the elongated slot 44 and a depending tab 53 on the escapement pawl 43 moves over an extension 54 on the holding pawl. The tab' 53 and extension 54 define a latch which maintains the tip portion 51 of holding pawl 50 in elevated position with respect to the tip portion 46 of escapement pawl 43 and prevents the holding pawl 50 from dropping down and engaging a pin 35 before the escapement pawl 43 has been returned to its original position. When the escapement pawl 43 is pushed to the rear by the next adjacent set pin 35 so that the forward edge of slot 44 abuts pin 45, the tab 53 on this pawl has moved from extension 54 of the holding pawl and the tip 51 of the holding pawl 50 drops down behind the set pin engaged by the escapement pawl. The escapement pawl assembly is again in the initial condition shown in FIGURE 2 of the drawings and ready for another escapement operation. During certain machine functions, such as carriage return and tabulation, it is desirable to remove both the escapement and holding pawls 43 and 50 from engagement with the pin 35 for a short period of time and this is accomplished by imparting a driving force to bifurcated member 55 so that pawl release arm 56 moves clockwise and one arm of pawl release bellcrank 57 engages and lifts the escapement and holding pawls. The other arm of the pawl release bellcrank is pivoted to the pawl release lever 56 intermediate its ends.

Positioned directly in front of the escapement pawl assembly 40 is the pin setting assembly 41 which is responsive to the actuation of the character escapement selection apparatus 27 when the typist selects a character or other machine function. The pin setting assembly 41 is operative to position the pins 35 to define the angular distance through which the pin wheel 30 is allowed to rotate during an escapement operation. This assembly comprises a pair of generally U-shaped pin setting arms 58 and 59 mounted for pivotal movement on spaced studs 60. Each of the arms has an upper portion 61, a vertically extending intermediate portion 62 and a lower portion 63. The forward ends of the lower portions 63 of the arms 58 and 59 are spanned by tension spring 64 while inwardly directed extensions on the forward ends of the upper portions 61 of the arms are pivotally connected to each other and a pull link 66. The arm 58 has an inwardly directed pin setting projection 67 formed on the intermediate portion 62 thereof and a similar pin setting projection 68 is provided on the vertically extending intermediate portion 62 of the pin setting arm 59. The pin setting projections 67 and 68 are located on opposite sides of the pin wheel 30 and are vertically spaced with respect to each other. The arms 58 and 59 and pull link 66 define a generally U shaped toggle-type linkage system which nestingly receives a portion of the outer periphery of the pin wheel. When a pulling force is applied to pull link 66, the pin setting projections 67 and 68 move inwardly to insure that the pins 35 adjacent these projections are either maintained in or moved to predetermined states.

Disposed in nesting relation between the arms 58 and 59 are a pair of pin setting mechanisms 70 and 71. The mechanism 70 comprises a pair of pin setting interposers 72 and 73 each having a pin setting projection 74 thereon. The interposers 72 and 73 are pivotally joined by a lever 75 which in turn is pivotally mounted on a stud 76 disposed between the studs 60. A pull link 77 is connected to the interposer 72 while the ends of the interposers 72 and 73 adjacent the stud 76 are spanned by a tension spring '78. The rear end of interposer 72 has a notch 79 formed therein. The vertically extending intermediate portions 62 of the pin setting arms 58 and 59' have slots therein for receiving and guiding the ends of the interposers 72 and 73, respectively. In essence, the interposers 72 and 73, lever 75 and pull link 77 define a shiftable scissor-like linkage. This linkage is biased by a spring 87 wrapped around the mounting stud 76- so that in the normal or unactuated position of the linkage as shown in FIGURE 2 of the drawings, the projection 74 on interposer 72 is positioned to engage one of the pins 35 carried by the pin wheel 30 when a pulling force is applied to pull link 66. The projection 74 on the other interposer 73 is positioned forwardly of the pin wheel 30 whereby it does not engage a pin when the rear ends of pin setting arms 58 and 59 swing inwardly. However, if a pulling force is applied to the pull link 77, the projection 74 on interposer 72 is retracted to a position where it does not engage a pin and the projection 74 on interposer 73 is moved to a position where it is operatively associated with the pin. The linkage is latched in this actuated position due to the notch 79 in the forward end of the interposer 72. As the interposer 72 moves rearwardly when pull link 77 is actuated, the edge of the notch 79 passes the intermediate portion 62 of the pin setting arm 58 and this interposer is immediately forced outwardly under the action of spring 78 to latch the linkage in its actuated position. The condition of the scissor-like linkage is determined by whether or not a pulling force is applied to pull link 77 and the condition of this linkage controls whether a pin 35 positioned adjacent the interposers 72 and 73 is maintained in or moved to a set or a reset state.

The pin setting mechanism 71 is generally the same as the pin setting mechanism 70 in that it comprises a pair of pin setting interposers 80 and 81 each having a projection 83 disposed on opposite sides of the pin wheel. The interposer 81 also has a notch 7 9 therein which performs the same latching function as the notch 7 9 in interposer 72. A lever 84 pivoted to stud 76 joins the opposite ends of the interposers 80 and 81 and a tension spring 85 is provided. The spring 87 wrapped about the stud 76 biases the pin setting mechanism 71 to the position shown. A pull link 86 is connected to the interposer 81 and, when a pulling force is applied to this link, the projection 83 on interposer 81 moves from and projection 83 on interposer 80 moves into operative pin setting relation with respect to a pin on the pin wheel. The intermediate portions 62 of the pin setting bars 58 and 59' are notched to receive the interposers and 81 and guide the longitudinal shifting movements thereof.

As mentioned above, actuation of the pull links 77 and 86 cause shifting movements of the pin setting mechanisms 70 and 71 and these mechanisms are latched in their actuated states clue to the provision of notches 79 in the ends of interposers 72 and 81. It is necessary to provide a means for unlatching the pin setting mechanisms and this is accomplished by providing a pair of stationary stops 88 (see FIGURE 4) disposed on opposite sides of the pin setting mechanisms 70 and 71 and adapted to engage at least the interposers 72 and 81. As will be later explained, the intermediate vertical portions 72 of the pin setting arm 58 and 59 move inwardly toward each other to effect setting of the pins and then outwardly past their initial or home position. As the pin setting arm on which one of the interposers is latched moves outwardly past its home position, the interposer abuts against its associated stop 88. This effectively disengages the pin setting arm from the interposer and the pin setting mechanism is automatically and immediately returned to its unactuated state by spring 87.

It should be understood that the above described arrangement for actuating and latching the pin setting mechanisms is not the only one which can be employed. For example, prior to a pin setting operation, the pin setting mechanisms could all be moved to their latched states. Thereafter, and prior to the inward movement of the pin setting arms 58 and 59, selected ones of the pin setting mechanisms would be released from the latched state by applying pulling forces to corresponding ones of the pull links in accordance with the character selected by the typist and the operation of the character escapement selection apparatus 27.

When the pin wheel 30 is at rest, four of the pins are positioned within the confines of the pin setting assembly 41 and these four pins are located directly in front of the set pin engaged by the escapement and holding pawls 43 and 50. If the pin setting assembly is in the position shown in FIGURE 2 of the drawings and a pulling force is applied only to pull link 66, the first pin in the pin setting assembly, designated 35', will be maintained in or moved to its reset state by the projection 67 on the pin setting arm 58. The second pin 35 will be engaged by the operative projection 74 on interposer 72 and maintained in or moved to its reset state. The projection 74 on the interposer 73 is in a position where it cannot engage the pin 35 since pull link 77 has not been actuated. The third pin 35" at the pin setting assembly will be maintained in or assume a set state since it is adapted to be engaged by projection 83 on the interposer 81 and cannot be engaged by projection 83 on interposer 80. The fourth pin 35"" at the pin setting assembly is maintained in or moved to its set state by the projection 68 on the intermediate portion of pin setting arm 59. When the pull link 66 is released and the pin setting assembly returns to its original condition, the first and second pins 35' and 35" will 'be in the reset state and the third and fourth pins 35" and 35"" will be in the set condition. Tripping the holding and escapement pawls 50 and 43 will permit the pin wheel 30 to advance through an angular distance corresponding to three basic escapement units since the rotation of the pin wheel is not arrested until the third pin 35", which is the next adjacent set pin, engages and returns the escapement pawl.

The amount of angular rotation of the pin wheel 30 during an escapement operation is regulated and varied in accordance with the operation of the pin setting mechanisms 70 and 71. If pull link 77 is pulled prior to inward movement of the pin setting arms 58 and 59, then pin 35" will assume a set state and the pin wheel will rotate a distance corresponding to two basic escapement units. Actuation of pull link 86 associated with pin setting mechanism 71 will cause pin 35' to assume a reset state and a movement of the pin wheel corresponding to four basic escapement units will take place during the next escapement operation. It should be noted that the first pin 35 is always reset and the fourth pin 35"" is always set whereby the pin wheel must at least move through a distance corresponding to two basic escapement units and cannot rotate through a distance equal to more than four basic escapement units during an escapement operation. The condition of the pull links 66, 77 and 86 and the states of the pins at the pin setting assembly 41 in providing various numbers of escapement units is set forth below in tabular form.

As successive escapement operations take place, the pins 35 on pin wheel 30 are advanced in an intermittent manner to the pin setting assembly 41. It should be noted that the pins are not automatically returned to any one state after an escapement operation takes place. Rather, the pins 35 about the periphery of the pin wheel 30 maintain the positions and states to which they were set by the pin setting assembly until they are again advanced to this pin setting assembly. The pin wheel and the pins define a limited memory which has information corresponding to past escapement operations stored therein. This is extremely valuable in accomplishing backpacing and forwardspacing operations on a character-by-character basis as will be later explained.

Character escapement'selection apparatus The character escapement selection apparatus 27 is shown in FIGURE 1 of the drawings and is operative to control the actuation of the pull links 66, 77 and 86 of the pin setting assembly 41 in accordance with the number of basic escapement units associated with a character selected by the typist. This apparatus actuates pull link 49 to release the escapement and holding pawls 43 and 50 from engagement with the pins 35 carried by the pin wheel 30. Means for initiating and controlling auxiliary machine functions such as spacing, backspacing, forwardspacing, case shift and the like are also provided.

As indicated above, each of the character keylevers 21 is associated with two of the characters formed on the print element 11 with the condition of the case shift keylever, not shown, determining which of the characters is selected when the character keylever is depressed. Disposed directly below each character keylever is a character interposer 90 and these interposers are arranged in aligned side-by-side relation. Extending transversely below the character interposers 90 are a plurality of character selector bails 91 which are adapted at certain times to be engaged and moved by coded projections 92 on the interposers.

The operation of the character keylevers 21 and interposers 90 during the character selection step of a printing operation can be generally summarized as follows: When a character keylever 21 is depressed, the corresponding character interposer 90 is moved downwardly and latched. Downward movement of the interposer operates a bail, not shown, which in turn releases the cycle clutch to complete a driving connection between an electric motor and filter shaft 93. Filter shaft 93 is rotated through 180 degrees and an extension thereon engages and moves forward the depressed interposer. The forward movement of the interposer causes rotation of certain of the character selector bails 91 in accordance with the coded projections 92 on the interposer. The character selector'bails 91 actuate apparatus, not shown, for rotating and tilting the print element 11 to bring the selected character into printing position. A complete description of this operation and the apparatus for accomplishing the same is contained in the above mentioned IBM Selectric typewriter instruction manual and particularly on pages 33-43 thereof.

Extending across the typewriter keyboard and transversely with respect to the character interposers are two and four unit character escapement selector bails 94 and 95. Those interposers associated with characters assigned four basic escapement units have operating projections 96 thereon. When an interposer corresponding to a character requiring four basic escapement units is moved forward by rotation of the filter shaft 93, the four unit character escapement bail is rotated in the clockwise direction to pull a link 97 which, acting through a flexible wire 98, causes actuation of pull link 86 of the pin setting assembly 41.

The two unit character escapement selector bail 94 is operated in a slightly different manner when compared to the arrangement employed in connection with four unit selector bail 95. The two unit selector bail 94 has a plurality of depending flags 100 of different widths attached thereto that are adapted to be engaged by projections 101 on the character interposers 90. When a projection 101 engages a flag 100 in response to forward movement of an interposer 90 by the filter shaft 93, the bail 94 is rotated and a pulling force is transmitted via wire 102 to the pull link 77 of the pin setting assembly 41.

The pull link 66 controlling the inward movement of the pin setting arms 58 and 59 and the pin setting interposers, 72, 73 and 80, 81 must be actuated during each pin setting operation. A flexible wire 103 extends to a latch member 104 having an elongated aperture 105 there in and mountedfor horizontal and pivotal movement with respect to a pivot pin 106. The latch member 104 is biased toward the rear of the typewriter by a spring 107 and has a step 108 thereon which is engaged by a flattened arm of a bellcrank' 109. The other arm of the pivoted bellcrank 109 carries a cam follower roll 110 which engages the periphery of a pin setting cam 111 mounted on a shaft 112 which is drivingly coupled with filter shaft 93. During a pin setting operation, pin setting cam 111 rocks bellcrank 109 in a counterclockwise direction. The latch member 104 is moved toward the front of the typewriter and the pull link 66 is pulled via wire 103 to actuate the pin setting asesmbly. The shape of pin setting cam 111 is such that during the restoring portion of the operation the latch member 104 moves rearwardly past its home position under the action of spring 107 until the forward end of elongated slot 105 engages pin 106. The flattened arm on the bellcrank 109 then moves forwardly and returns the latch member 104 to its initial or home position. In this manner, the pin setting assembly 41 receives a snap-like restoring force which insures the opening of the pin setting arms past their home or rest positions to unlatch the previously actuated pin setting mechanisms.

During certain typewriter operations, such as forwardspacing, when it is necessary to suppress the operation of the pin setting assembly 41, a bail 115 is rotated in 'a counterclockwise direction to move a release lever 116. Release lever 116 pivots latch member 104 in a counterclockwise direction about pivot-pin 106 so that the driving connection between this latch member and the flattened arm of bellcrank 109 is broken and no pulling force is transmitted to pull link 66. The latch member 104 is moved rearward under the action of spring 107 until the edge of slot 105 engages pin 106 and the step 108 is reengaged by the flattened arm of bellcrank109 during the for ward restoring movement thereof. The apparatus for rotating the pin setting suppress bail 115 will be described in following sections of the specification. If desired, the release lever 116 and lever 104 can be designed to insure that theactuation of the pin setting assembly is suppressed during only one cycle of operation regardless of how long the bail 115 is retained in its rotated state.

After the pin setting assembly has been actuated, the escapement and holding pawls 43 and 50 must be released to allow the pin wheel 30 to rotate through an angular distance corresponding to the number of basic escapement units associated with a selected character. The shaft 112 also carries a properly contoured escapement cam 117 which is engaged by escapement cam follower roll 118 mounted on one arm of escapement bellcrank 119. The other arm of escapement bellcrank 119 is attached to a flexible wire 120 which extends to pull link 49. When the cam shaft 112 is rotated, and after actuation of the pull link 66, the pull link 49 receives a pulling force to operate escapement pawl assembly 40. The pin wheel 30 rotates until the next set pin 35 engages and returns the escapement pawl 43 to its original position.

When the case shift mechanism for the typewriter is operated whereby upper case characters are selected when the character keylevers 21 are depressed, it may be desirable to shift or change the number of basic escapement units associated with a particular character keylever. For example, a lower case 1 may belong to the group of characters assigned two basic escapement units and the upper case or capital L to the character group requiring three basic escapement units. To accomplish such a conversion when the case shift mechanism is actuated, the two unit character escapement selector bail 94 is mounted for transverse movement with respect to the interposers 90 whereby the positions of the flags 100 with respect to the projections 101 on the associated character interposers 90 are changed. Located on the right side of the typewriter is a pivoted shift crank 129 which is engaged by one end of two unit character escapement selector bail 94 due to the force exerted by leaf spring 121 on the other end of the bail. When the case shift keylever is depressed, suitable mechanism not shown, is actuated to cause a clockwise movement of shift arm 122 and print element 11 is rotated through 180 degrees via tape 123. For a complete description of the case shift mechanism, reference should be had to pages 63-70 of the above mentioned IBM Selectric typewriter instruction manual. The movement of shift arm 122 is supplied to shift crank 129 by way of linkage 124 and two unit character escapement selector bail 94 moves to the left from the position shown in FIGURE 1 of the drawings against the force exerted by leaf spring 121.

The effect of this shifting of the two unit selector bail 94 is to move the thinner of the flags 100 to a position between the interposers where the same cannot be engaged by interposer projections 101. An interposer projection 101 which engages a thin flag 100 when the case shift apparatus is not actuated to cause an escapement of two basic escapement units will not operate the bail '94 when the case shift mechanism is actuated so that an escapement movement corresponding to three basic escapement units takes place. This is due to the fact that actuation of pull link 66 during each pin setting operation by latch 104, cam 111 and bellcrank 109 automatically conditions the pins at the pin setting asesmbly to provide an escapement movement of three basic escapement units. If it is desired that no change in the escapement movement takes place when the case shift mechanism is actuated, then the flag 100 associated with a particular character interposer is made wide enough whereby the projection 101 on the interposer always engages the flag.

In the typewriter it is necessary to provide space bar means for advancing the carrier 15 and the print element 11 by a predetermined distance without effecting printing to provide spaces between words and the like. Such spacing is accomplished in the present instance by providing a two unit space bar 125 and a three unit space bar 126. Operation of space bar 125 lowers keylever 127 and this keylever in turn actuates an interposer having a projection 101 formed thereon. A wide flag 100 is associated with the two unit space bar interposer so that two unit character escapement selector bail 94 is rotated and the second pin 35 in the pin setting assembly 41 is maintained in or moved to its set state. The character escapement selector bails 94 and 95 are not actuated when three unit space bar 126 is operated since the interposer associated with three unit keylever 128 is effective only to connect the filter shaft 93 and cam shaft 112 for rotation which automatically results in the pin setting mechanism being conditioned to provide a movement corresponding to three basic escapement units.

The escapement control apparatus 26 and the character escapement selection apparatus 27 are relatively simple in construction and operation. These systems are also highly versatile in that the same can be adapted to operate with almost any escapement scheme with a minimum of design change. For example, the pin setting assembly 41 and the character escapement apparatus may be expanded or contracted by including more or less of the character escapement selector bails and the pin setting mechanisms each including a pair of pin setting interposers in accordance with the number of basic escapement movements required. The pin setting assembly can be constructed so a basic or standard escapement movement corresponding to more or less than three escapement units is provided when the filter and cam shafts are rotated. Obviously, the coding of the interposer projections and flags on the two unit escapement selector bail can be readily changed. Also, any or all of the character escapement selector bails may be mounted for shifting movement in a manner similar to the two unit bail to permit an almost unlimited range of escapement movement changes when the case shift mechanism is actuated.

Backspacing apparatus One of the primary advantages of the disclosed typewriter is that the typist is provided with a means of backspacing on a character-by-character basis utilizing the previous escapement information stored in the pin wheel. In general, the backspacing apparatus comprises backspace keylever means which, when operated, actuates drive means for rotating the pin wheel 30 in a direction opposite to the direction indicated by the arrow 39 through incremental angular distances each corresponding to a basic escapement unit. The incremental movement of the pin wheel continues automatically with the carrier and the print element moving in the backspace direction until the adjacent previously set pin on the pin wheel engages and operates pin sensing means. The pin sensing means de-energizes the drive means for the backspacing apparatus and the print element is located at the previous printing position. Repeated actuation of the backspace keylever by the typist will automatically move the carrier and print element in the backspace direction to successive printing positions.

The backspacing apparatus is shown generally in FIG- URES 1 and 5 through 7 of the drawings. A backspace keylever 130 is provided at the keyboard and a backspace keylever pawl 132 is pivotally attached to this keylever. The backspace keylever pawl 132 is biased upwardly and rearwardly by a tension spring 133.

Downward movement of the backspace keylever pawl 132 in response to depression of backspace keylever 130 causes counterclockwise pivotal movement of lever 134 about its pivot pin 135 since a tab 136 on the pawl engages the lever 134 at this time. The pivoting movement of the lever 134 results in downward vertical movement of latch 137 due to the pivotal connection at 139 between the lever 134 and latch 137. The latch 137 is biased for counterclockwise rotation independently of lever 134 by spring 140 and has a pair of steps 141 and 142 formed on the upper edge thereof. The steps 141 and 142 provide abutment or stop surfaces and, in the initial condition of the apparatus, the stop surface 141 engages a stationary stop plate 143. The generally vertical movement of latch 137 continues until the stop surface 141 clears 13 the lower edge of the stop plate 143. The spring 140 gains control and immediately pivots the latch 137 counterclockwise until the second stop surface 142 abuts against the edge of stop plate 143.

The rocking movement of the latch 137 performs a plurality of functions simultaneously. A link 144 connected to the rear of the latch is moved forwardly to actuate a pin sensing assembly generally designated by reference numeral 145 (FIGURE 7) whose operation will be hereinafter more fully described. A transversely extending tab 146 on a forwardly projecting arm 147 of the latch 137 engages the backspace keylever pawl 132 and moves the same forwardly whereby the keylever pawl is positioned and maintained out of driving engagement with lever 134. The manner of operation is such that the latch 137 is effectively latched and maintained in its rotated position with the stop surface 142 engaging the lower edge of stop plate 143.

The forwardly projecting arm 147 of the latch 137 engages a transversely extending tab 148 formed on an interposer latch 149 to move this latter member in'a counterclockwise direction when the latch 137 rotates. The interposer latch 149 is pivotally connected to an elongated backspace interposer 150 at 151 and is spring biased for clockwise movement by tension spring 152. In the normal or rest condition of the apparatus, a vertical stop surface 153 on the interposer latch 149 abuts against the lower edge of stop plate 143 so that the interposer 150 is maintained in its forward position. Pivoting of interposer latch 149 by the latch 137 releases the backspace interposer 150 and it is free to move rearwardly and downwardly under the action of interposer spring 154. v

The rearward movement of the backspace interposer 150 actuates a bail 155 which in turn causes pivotal movement of clutch releasearm 156. A clutch 157 engages so that a double lobed backspace cam 158 mounted on a power driven operational cam shaft 159 is rotated through 180 degrees. A cam check pawl 160 is provided to prevent backward creep of the backspace cam 158 and the resulting noise. The clutch 157 and the means employed for actuating the same are similar to the arrangement presently employed in the IBM Selectric typewriter and those desiring a more detailed explanation of the structure and operation should have reference to the above identified instruction manual, and particularly to pages 7990 thereof.

The backspace cam 158 is engaged by a cam follower roll 161 carried at the upper end of a pivoted cam follower lever 162. The cam follower roll 161 will move first rearwardly and then forwardly as the backspace cam The mechanism connected to the link 164 for rotating the pin wheel is shown in FIGURE 6 of the drawings and comprises a bellcrank 168 journalled on shaft 31 mounting the pin wheel. Pivotally attached to an arm of the 158 is rotated and this motion is transferred via bellcrank 163 to a link 164. The movement of link 164 actuates mechanism to be later described which causes rotation of the pin wheel 30 in the backspace direction. The cam follower lever 162 itself has a cam surface 165 thereon which, through .cam follower 166 and backspace interposer reset bellcrank 167 is operative to move the backspace interposer 150 forward toward its initial position against the action of interposer spring 154. Forward movement of the backspace interposer 150 carries the interposer latch 149 to a position where its stop surface 153 is positioned forwardly of the stop plate 143. However, if the latch 137 is still in its rotated position, the stop surface 153 is spaced below the stop plate 143 due to the position of latch arm 147 and the interposer 150 is free to move to the rear under the action of spring 154 to again cause rotation of backspace cam 158 and operation of the mechanism for advancing the pin wheel 30 another basic escapement unit in the backspace direction. The pin wheel is automatically rotated through successive angular distances each corresponding to a basic escapement unit until the latch 137 has returned to its original condition whereby the interposer latch 149 can engage and be latched on the stop plate 143 to prevent further rearward movement of backspace interposer 150.

bellcrank 168 is a backspace pawl 169 which is biased by spring 170 into engagement with the pins 35 carried by the pin wheel. The backspace pawl 169 is positioned over the circumferential edge slot 52 in the pin wheel 30 so that it is adapted to engage each of the pins 35 regardless of the state thereof. A pulling force on link 164 rotates bellcrank 168 clockwise and the backspace pawl 169 moves the pin wheel clockwise (opposite to the direction indicated by arrow 39) through an angular distance sufficient for holding pawl 50 to move over and engage the next adjacent one of the pins in the backspace direction. The holding pawl 50 maintains the pin wheel in this position against the force exerted by the constant torque device 25 through the lead screw 18 and pitch changing apparatus 28 even if the pin on the pin wheel is not set since, as previously explained, the holding pawl 50 is adapted to engage each of the pins 35 regardless of its state. Return counterclockwise rotation of the bellcrank 168 moves the backspace pawl 169 over one of the pins and this pawl is again ready to advance the pin wheel in a backspace direction by an angular distance corresponding to the basic escapement unit.

The pin sensing assembly 145 is mounted on one side of the bracket 32 and comprises a sensing finger 171 formed on and carried by a sensing lever 172. The sensing finger 171 is movable forwardly into and then rearwardly from the path of travel of the set pins 35 carried by the pin wheel at a position located directly in front of the escapement and holding pawls 43 and 50. The sensing finger 171 moves intothe path of travel of the set pins at the beginning of a backspace operation in response to actuation of backspace keylever means and is engaged by the next set pin as the pin wheel is moved in the backspace direction. The set pin moves the pin sensing finger 171 and this is operative to terminatea backspace operation with the print element positioned at a previous printing position. Further, the sensing finger is automatically retracted from the path of travel of the set pins.

As mentioned above, the counterclockwise movement of latch 137 when backspace keylever is depressed exerts a pulling force on link 144. Forward movement of link 144 rotates a lever 173 clockwise about eccentrically mounted pivot pin 174. A hump 176 on the lower end of lever 173 immediately engages an extension 177 on the pin sensing lever 172 and the pin sensing finger 171 is advanced into the path of travel of the set pins carried by the pin wheel against the action of spring 175. The pin sensing finger 171 moves in a straight line due to the design of the parts including the loose mounting of the pin sensing lever 172 with respect to pivot pin 174 and the sliding connection of the pin sensing lever 172 with respect to mounting stud 178. As the pin sensing finger 171 completes its straight line movement into the path of travel of the set pins, the forward end of a latch 179 drops down behind this finger under the urging of tension spring 180.

The finger 171 is maintained in the path of travel of the set pins by latch 179 as incremental backspacing movements of the pin wheel automatically occur. Eventually, the finger 171 is engaged by the next adjacent set pin 35 in the backspace direction and the sensing lever 172 is rotated counterclockwise about the pivot pin 174. The lever 173 is also rotated in this direction because of the engagement of transversely extending tab 182 of lever 173 by tip 181 on the pin sensing lever 172. This causes a rearward pulling force to be exerted via link 144 to latch 137 which is greater than the force exerted by tension spring tending to maintain the latch in its latched condition. Latch 137 moves rearwardly until the abutment surface 141 clears the bottom edge of the stop plate 143 and then moves vertically under the combined action of the hairpin spring engaging lever 134 and the pulling force of link 144 until it is restored to its initial condition with stop surface 141 engaging stop plate 143. This per-. mits the interposer latch 149 to restore when the backspace interposer 150 is returned forward a short time later under the action of backspace interposer reset bellcrank 167 and ends the character back-space operation. Also, the extension 136 of keylever pawl 132 is allowed to return to its original driving relation with respect to lever 134 by tension spring 133 either automatically or whenever the typist releases the backspace keylever 130.

The sensing finger 171 is moved in an arc about the stud 178 as pin sensing lever 172 rotates in a counterclockwise direction when this finger is engaged by a set pin. Eventualy the pin sensing finger 171 reaches a point where it is no longer engaged by the latch 179. However, the balance between the spring forces of springs 175, 180 and 140 and the dynamic forces generated between the moving set pin 35 and sensing finger 171 are such that the pin sensing assembly 145 does not immediately collapse. The pin wheel 30 experiences dynamic overthrow and it is not until the pin wheel begins to return from its overthrow position toward its final rest position with the set pin returning toward the holding pawl 50 that the spring forces gain control and move the sensing finger 171 from the path of travel of the set pins to collapse the pin sensing assembly. The pin sensing assembly is again in its initial state and ready for another cycle of operation when backspace keylever 130 is depressed.

It should be apparent that the backspacing apparatus ofiers many advantages. The apparatus is so arranged that once the typist depresses the backspace keylever below a definite and defined trip point, a backspace operation takes place in an automatic and uninterrupted fashion. The typist cannot stop or inadvertently interrupt a backspace operation once the same has been initiated. The print element and carrier are moved in incremental steps each corresponding to a basic escapement unit in the backspace direction until the adjacent prior printing position is reached. The timing and arrangement of the elements is such that the print element always stops at a position corresponding to a previous print position The straight line movement of sensing finger 171 insures that proper entry is made in the small spaces between the pins but yet the design of the system provides for arcuate movement of the sensing finger when the same is engaged by a set pin. This provides a relatively large and extended movement for actuating the connecting link 144 and latch 137 while eliminating the necessity of precise adjustment of the pins and the backspace apparatus with respect to each other. Further, the backspace apparatus is primarily responsive to the displacement of the set pins and is not sensitive to changes in velocity or acceleration of the pin wheel.

The above described backspacing apparatus per se, including the backspace keylever means and the pin sensing apparatus, is disclosed and claimed in copending application of George A. Holt and Charles N. Van Avery, Ser. No. 311,375, filed Sept. 25, 1963 This latter application is entitled Backspacing Apparatus for Proportional Escapement Typewriter, and is assigned to the assignee of the present invention. Reference may be made to this copending application for more information concerning the operation and advantages of the disclosed backspacing apparatus since the apparatus has been described in the present application only to the extent necessary to provide an understanding of the construction and operation of the overall typewriter.

F orwardspacing apparatus In the normal use of the backspacing apparatus in correcting a mistake, the print element and carrier would be moved in the backspace direction on a character-bycharacter basis until the print element is at the previous printing position corresponding to the character in error.

The erroneous character is then corrected by erasing and/ or overstriking. It is now desired to advance the print element and carrier to the last or furthest printing position so that normal typing can be resumed. The pin wheel 30 contains the character escapement information corresponding to each of the character selection operations and printing positions which are located between the printing position corresponding to the erroneous character at which the print element is located and the last or furthest printing position. This permits the print element to be advanced on a character-by-character basis by actuating the escapement assembly 40 while suppressing the operation of the pin setting assembly 41.

A forwardspace keylever 185 on the typewriter keyboard has a hook-like projection 186 thereon which engages the pin setting suppress bail as is shown in FIGURE 1 of the drawings. Downward movement of the forwardspace keylever 185 causes rotation of pin setting suppress bail 115 which engages and depresses two unit space bar keylever 127. As a result, a pulling force is applied via flexible wire to the pull link 49 so that the escapement assembly 40 is actuated. The rotation of pin setting suppress bail 115 prevents the pin setting arms 58 and 59 from swinging inwardly as has been previously described. Repeated actuation of the forwardspace keylever causes the print element to advance on a character-by-character basis to the last printing position. It is noted that the time consuming and tedious alignment procedures usually associated with correcting errors in conventional proportional escapement typewriters are completely eliminated due to the use of stored escapement information to permit backspacing and forwardspacing on a character-by-character basis.

Pitch changing apparatus The pitch changing apparatus 28 is disposed between the lead screw 18 and the escapement control apparatus 26 and provides an adjustable gearing means for regulating the distance travelled by carrier 15 and interchangeable print element 11 for each basic escapement unit. While the escapement control apparatus 26 defines the absolute number of basic escapement units associated with an escapement operation, the pitch changing apparatus 28, under typist control, determines the actual distance moved by the carrier 15 and print element 11. This apparatus provides the typist with a means for changing the escapement pitch to vary the appearance of material printed with the same print element or to allow the printing of material with various size type styles formed on different print elements. For example, relatively small size characters forming a particular type style will usual- 1y be printed with a larger pitch (a larger number of characters printed in a predetermined distance) than the relatively large size characters making up a different type style.

As shown in FIGURES 8 and 9 of the drawings, the shaft 31 mounting the pin wheel 30 extends through a side plate of the mounting bracket 32. Keyed or otherwise rigidly attached to the projecting end of the shaft 31 in aligned side-by-side relation are three pinion gears 192-194 each having the same number of teeth and, as a consequence, different pitches (the number of teeth per unit distance of pitch circumference). Meshing with the pinion gears 192-194 are pitch gears 195-197 each having the same pitch as the corresponding one of the pinion gears 192494. The pitch gears 195197 are mounted for independent rotary movement on and with respect to the shouldered end portion 198 of shaft 199. Means, to be later described, are providal for detachably securing any selected one of the pitch gears 195-197 in driving engagement with the shaft 199. The pitch gears 195197, in combination with the pinion gears 192-194, define three selectable gear sets each capable of drivingly intercon meeting the shafts 31 and 199.

The selected one of the gear sets 192, 195; 193, 196;

1 7 or 194, 197 which drivingly interconnects the shafts 31 and 199 determines the extent of actual movement of the carrier and print element for each basic escapement unit. The shaft 31 mounts the pin wheel 30 while the shaft 199 is connected by a gear train comprising gears 200-202 to lead screw 18. For example, when gear set comprising gears 194 and 197 is selected, the lead screw 18 will rotate through a greater angular distance for a predetermined angular movement of the pin wheel 30 than if either of the other gear sets had been selected under the same condition. Similarly, if the gear set comprising gears 193 and 196 is selected, the carrier and print element move through a greater distance for the predetermined angular movement of pin wheel 30 than when the gear set including gears 192 and 195 operatively interconnects the shafts 31 and 199.

The shouldered end portion 198 of shaft 199 has an elongated slot 203 therein extending beneath the axially aligned and independently rotatable pitch gears 195-197. Received within the slot 203 is a key 204 having a rounded end portion 205 which is pivoted to an annular operating member 206. A leaf spring 207 is received in the slot 203 and exerts a biasing force on the key 204 tending to move the end portion 205 thereof radially outward from the slot. Each of the pitch gears 195-197 has a plurality of circumferentially spaced and radially extending. slots 208 disposed about the inner periphery thereof. The slots 208 are provided for receiving the rounded end portion 205 of the slidable key 204. Also, the inner peripheral edges of the pitch gears 195-197 are beveled at 209 to facilitate movement of the key 204 and selective engagement of the pitch gears as will be later explained.

Extending into a circular slot 210 in the annular operating member 206 are a pair of vertically spaced arms 211 of U-shaped actuator 212. The actuator 212 is mounted for pivotal movement on a stud 213 whose axis'extends transversely with respect to the axis of the shaft 199. An extension of the actuator 212 projects transversely into the space between the arm portions 214 of a U-shaped pivoted member 215. One arm 214 of the member 215 is operatively connected to a typist-controlled pitch selection lever 216 via link 217, fitting 218 and shaft 219. The arrangement is such that when the typist rotates the pitch selection lever 216, the annular operating member 206 is moved axially on the shaft 199 to disengage the key 204 from one of the pitch gears and move this key to a position where another of the pitch gears is drivingly connected to shaft 199.

Detent means for holding the apparatus in a selected pitch position is provided. This detent means comprises three axially aligned recesses 220 in the shouldered portion 198 of shaft 199. Cooperating with the recesses 220 are a pair of balls 221 received in a radial aperture 222 in the annular operating member 206. The balls 221 are forced into locking engagement with the recesses 220 by lever 216 and movement of the key' 204 to select a different gear set, a slot 208 in the selected one of the pitch gears will not be aligned with the rounded end portion 205 of the key 204. In this case, the end portion 205 of the key is cammed downwardly by the adjacent beveled edge 209 of the selected pitch gear against the action of leaf spring 207. The slot 203 in the shaft 199 is deep enough to allow the end portion 205 of the key 204 to be moved to a position directly below the selected pitch gear. At this time, none of the pitch gears 195-197 will be drivingly connected to shaft 199. Since the pin wheel 30 and escapement assembly 40 are effectively disconnected from the system, the constant torque device 25 will rotate shaft 199 via lead screw 18 and idler gears 200-202 until a slot 208 in the selected pitch gear passes over the end portion of the key. The leaf spring 207 immediately forces the end portion 205 of the key 204 into this slot and the selected pitch gear is drivingly connected to shaft 18 199. The design of the key 204, pitch gears -197 and the detent means is such that it is impossible to connect two of the pitch gears to the shaft 199 at any one time.

Since the pitch changing apparatus provides a means for selectively varying the distance moved by the carrier and the print element for each basic escapement unit, it is necessary to provide a means for changing the scale presented to the typist. Also, as explained in previous sections of the specification, the pin wheel 30 provides a memory for information corresponding to only a limited number of past escapement operations. If full and effective use is to be made of the memory capability of the pin wheel 30 and the apparatus permitting backspacing and forwardspacing on a character-by-character basis, a visual indicator must be provided which shows the typist the amount of usable character information stored in the memory at any particular instant in time. The number of pins carried by the pin wheel is predetermined and this defines the number of basic escapement units available in storage. However, the visual indicator must be capable of being changed to indicate the extent of stored character information depending on the pitch selected by the typist. The apparatus for selecting or changing the pitch gears, the typist scale and the character storage indicator are all operated in conjunction with each other to provide the typist with the information necessary to make full use of the inherent capabilities of the typewriter.

As most clearly shown in FIGURE 1 of the drawings, a connecting link 225 extends from an arm 214 of the U-shaped pivot member 215 to a bellcrank 226 pivotally mounted adjacent the right hand side of the typewriter. A pin engages a slotted lever 227 carried on one end of a scale member 228. The scale member extends across the front of the typewriter and is disposed in cooperating relation with respect to a pointer 229 mounted from carrier 15. The scale member 228 has three sets of reference indicia formed thereon and located at circumferentially spaced points. The arrangement is such that when the pitch of the typing is changed by typist actuation of pitch selection lever 216, the scale member 228 is rotated to present the proper reference scale to the typist.

A character storage indicator 230 is provided by a cylindrical tube 231 (see FIGURES 10 and 11) which is open at each end and has inturned edges 232 along its length. The edges 232 are received in an elongated slot of the scale member 228 so that the character storage indicator is *slidable along and rotatable with the scale member. The tube 231 has a pair of window-like openings 23-4 and 235 in the front and back thereof. The side edges of the front window-like opening are stepped to define three different length portions while the sideedges of the rear window-like opening are tapered. Extending into the rear window-like opening 235 of the character storage indicator is a projection 237 mounted from the carrier 15 and movable With the pointer 229. The projection 237 is adapted to engage the tapered side edges of the rear window-like opening 235 and move the indicator 230 in either direction with the carrier and the print element. Since the indicator is rotatable with the scale member, a different one of the length portions in the front windowlike opening 234 is presented to the typist when the pitch selection lever 216 is actuated.

The pitch changing apparatus, the scale member and the character storage indicator by themselves and the specific sub-combinations thereof, do not form a part of the present invention but rather are disclosed and claimed in the copending application, entitled Pitch Changing Apparatus for Proportional 'Escapernent Typewriter. This application was filed in the U.S. Patent Office on Sept. 25, 1963, concurrently with the present application under Ser. No. 311,377, by Giannino Colombo and George A Holt, and is assigned to the assignee of the present invention. Only a description of the pitch changing apparatus, the scale member and the character storage indicator sufficient to permit an understanding of the overall typewriter is set forth in the present specification. However, it should be apparent that more or less than three of the gear sets may be provided and corresponding changes can be made in the scale member and the character storage indicator if it desired to have more or less than three basic pitch adjustments. The gear sets are driven from either side since during forward escapement operations the constant torque device 25 rotates the lead screw while during backspacing operations the pin wheel 30 is driven directly by the backspacing apparatus.

Constant torque device The constant torque device 25 is shown in FIGURES 1 and 12 of the drawings and functions to maintain a substantially constant torque on the lead screw 18. This device is the subject matter of co-pending application Ser. No. 311,376, filed on Sept. 25, 196-3, concurrently with the present application, entitled Constant Torque Drive Means for Typewriter, and which is assigned to the assignee of the present invention.

Mounted on the left end of the lead screw 18 is a pinion gear 240 whose teeth mesh with gear teeth formed about the outer periphery of an annular spring housing 241. The spring housing 241 is rotatably mounted on an elongated sleeve 242 which in turn is received over and rotatable with respect to an input shaft 243. The input shaft 243 is supported .for rotation by an annular collar 244 formed in a side plate 245 of the typewriter.

The spring housing 241 is generally cup-shaped and has an outwardly extending circular flange which, in combination with the sleeve 242, defines an annular recess for receiving a spiral spring 247. The spring is wound in such a fashion that the spring housing 241 is biased for counterclockwise rotation with respect to sleeve 242 and, as a consequence, the lead screw 18 is adapted to be rotated in a clockwise direction to permit movement of the carrier 15 and print element 11 whenever the escapement assembly 40 is actuated to allow the pin wheel 30 to rotate.

Rigidly mounted on the outer end of input 243 is a sleeve 248. Received in overlying and spanning relation with respect to the sleeves 242 and 248 is a clutch spring 249. The clutch spring 249 is right hand wound and has one end attached to the sleeve 242 while the other end provides a radially extending projection 250. An annular cover plate 251 covers the open end of spring housing 241 and has an outwardly extending clutch release arm 252 which, at certain times, is adapted to be engaged by the projection 25% of clutch spring 249.

Received in overlying and spanning relation with the collar 244 and the elongated sleeve 242 is a left hand wound clutch spring 253. One end of clutch spring 253 is connected to sleeve 242 while the other end defines a projection 254 which is adapted to be engaged by clutch release arm 255 carried by the spring housing 241. Means, not shown, are provided for oscillating the input shaft 2 43 once each escapement operation at a time prior to the actuation of the escapement apparatus.

In operation, the input shaft 243 is oscillated and as this member rotates in a counterclockwise direction the right hand wound clutch spring 249 provides a driving connection between the sleeves 248 and 242 to cause winding and tensioning of the spiral spring 247. The spring housing 241 cannot rotate at this time since the escapement pawl 43 engages one of the pins 35 and holds the pin Wheel 30. Also, the left hand wound clutch spring 253 slips to permit counterclockwise movement of the sleeve 242 and input shaft with respect to the collar 244. The spiral spring 247 is wound to a predetermined extent at which time the projection 250 of the clutch spring 249 engages clutch release arm 252. This releases the clutch spring 249 and breaks the driving connection between the input shaft 243 and the sleeve 242. The input shaft 243 can still rotate in the counterclockwise direction but the spiral spring 247 is not further wound after the projection 25% engages clutch release arm 252. Unwinding of the spiral spring 247 is prevented by clutch spring 253 which engages and holds the sleeve 242 to stationary collar 244 whenever a clockwise rotating force is applied to sleeve 242.

Eventually the input shaft 243 changes its direction of rotation. Clockwise rotation of the input shaft has no effect on the previously wound spiral spring 247 since right hand clutch spring 249 is not engaged under this condition. The clutch spring 253 prevents unwinding of the spiral spring 247. It should be apparent that the clutch springs 249 and 253 permit only uni-directional movement of the sleeve 242 to wind the spiral spring 247 to a predetermined extent in response to oscillating rotation of the input shaft 243. Also, once the spiral spring 247 has been wound to a predetermined extent, the clutch spring 249 is released to prevent further winding of this spiral spring.

During a backspacing operation, the lead screw 18 is driven in the opposite direction by the backspace apparatus. The spring housing 241 is rotated in a counterclockwise direction by pinion 240 and, since sleeve 242 is held stationary by clutch spring 253 at this time, the outer convolutions of the spiral spring are moved in a direction to wind the spiral spring. When the spiral spring 247 has been wound to a predetermined extent, the clutch release arm 255 engages projection 254 of clutch spring 253 to disengage the same. The spring housing 241, spring 247 and sleeve 242 then rotate as a unit during the remainder of the backspacing operation and the spiral spring is not further wound.

The constant torque device maintains a substantially constant torque of the lead screw 18 of the typewriter. The spinal spring 247 is designed to provide a relatively constant torque on the lead screw 18 of the typewriter, pected. The predetermined point to which the spring 247 is wound either by rotation of the input shaft 243 or the lead screw 18 is selected to provide a torque which will move the carrier and print element through the largest escapement distance within the time interval of an operating cycle alloted for escapement operations. The system is so designed that the total movements of the input shaft 243 and the lead screw 18 in the backspace direction are greater than the driving movements imparted to the lead screw 18 by the constant torque device.

Operation and conclusion The overall operation of the typewriter disclosed herein should now be apparent. When a typist selects a character by actuating a character keylever, the character escapement selection apparatus 27 actuates the pin setting assembly 41 to move the pins in accordance with the number of basic escapement units associated with the selected character. The escapement pawl assembly 40 then is operated to permit rotation of the pin wheel 30 in accordance with the distance between adjacent set pins. The movement of the pin wheel 30 is transmitted via the pitch changing apparatus 28 to permit movement of the carrier 15 and print element 11 through an escapement distance determined not only by the movement of the pin wheel but also by the setting of the pitch selection lever 216. The constant torque device rotates the lead screw 18 to move the carrier and print element .and maintains a substantially constant torque on the lead screw.

Of particular importance is the fact that the pin wheel 30 and pins 35 provide a limited memory for past escapement information. The memory capability of the typewriter allows backspacing and forwardspacing to be accomplished on a character-by-character basis. The tedious and time-consuming visual alignment techniques that characterize backspacing and forwardspacing operations with more conventional proportional escapement typewriters are eliminated.

While the invention has been particularly shown and de- 21 scribed with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that the foregoing and other changes in [form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. Escapement apparatus for use in a typewriter comprising:

a typewriter frame and a typewriter carrier;

a sing-1e print element having characters thereon removably mounted on said carrier;

character selection means for moving said print element to bring a selected character into printing position;

means to rock said print element to move said print element in a direction to eifect printing of a character in said printing position;

an elongated lead screw supported in said frame and having a driving connection with said carrier to control movement of said carrier and said print element with respect to said frame;

drive means operatively connected to and located adjacent one end of said lead screw tending to rotate the same in one direction;

a generally circular disc shaped pin wheel carrying a plurality of pins located adjacent the other end of said lead screw;

a plurality of selectable gear means each operative when selected to drivingly interconnect said lead screw and said pin Wheel;

each of said pins being movable to at least two positions defining at least two states and the distance between adjacent pins defining a basic escapement unit;

a plurality of character keylevers each associated with at least one of the characters to be printed;

a pin setting assembly located adjacent said pin wheel for moving and maintaining the pins adjacent saidpin setting assembly in selected states;

an escapement assembly comprising an escapement pawl mounted for pivotal and limited longitudinal movement for engaging those of said pins in one of said states to hold said pin wheel against rotation by said 'drive means; 4

means to pivot and remove said escapement pawl from engagement with said pins in said one state and then position said escapement pawl in the path of travel of said pins in said one state to permit rotation of said pin wheel and lead screw by said drive means to advance said carrier and said print element'until the next adjacent pin in said one state engages said escapement pawl; and

character escapement selection apparatus interconnecting said character keylevers, said pin setting assembly and said escapement assembly to actuate said pin setting assembly and said means to remove in the order stated after rocking of said print element to permit rotation of said pin wheel and corresponding movement of said carrier and said print element equal to the number of basic escapement units associated with a selected character.

' means to rotate said pin wheel in a direction opposite to the direction which said pin Wheel is rotated by said drive means; 7

backspace keylever means controlling the actuation of said means to rotate;

means to sense the presence of one of said pins in said one state; and

means responsive to said pin sensing means to de-energize said means to rotate said pin wheel in said direction opposite when said pin sensing means senses a pin in said one state to permit backspacing in accordance with the past escapement information represented by the states of said pins.

3. Escapeinent apparatus for use in a typewriter comprising:

a typewriter frame and a typewriter carrier;

an elongated lead screw supported in said frame and having a driving connection with saidcarrier to control movement of said carrier with respect to said frame;

drive means operatively coupled to and located adjacent one end of said lead screw tending to rotate the same in one direction;

a generally circular disc shaped pin wheel carrying a plurality of pins located adjacent the other end of said lead screw;

means drivingly interconnecting said lead screw and said pin wheel whereby said pin wheel is biased for rotation by said drive means;

each of said pins being movable to at least two positions defining at least two states and the distance between two adjacent pins defining a basic escapement unit;

,a plurality of character keylevers each associated with at least one of the characters to be printed;

a pin setting assembly located adjacent said pin Wheel for moving and maintaining the pins adjacent said pin setting assembly in selected states;

an escapement assembly comprising an escapement pawl mounted for pivotal and limited longitudinal movement for engaging those of said pins in one of said states to hold said pin wheel against rotation by said drive means;

means to pivot and remove said escapement paWl from engagement with said pins in said one state and then position said escapement pawl in the path of travel of said pins in said one state to permit rotation of said pin wheel and said lead screw by said drive means to advance said carrier until the next adjacent pin in said one state engages said escapement pawl; and

character escapement selection apparatus interconnecting said character keylevers, said pin setting assembly and said escapement assembly to actuate said pin setting assembly and said means to remove in the order stated to permit rotation of said pin wheel and corresponding movement of said carrier equal to the number of basic escapement units associated with a selected character.

4. Escapement apparatus for use in a typewriter comprising:

each of said elements being settable to at least two states;

an element setting assembly located adjacent said path for setting and maintaining the elements adjacent said element setting assembly in selected states;

an escapement assembly comprising a movable escapement member engaging those of said elements in one of said states;

means to remove said escapement member (from engagement with one of said elements in said one state to permit movement of said elements in said path and said driven member until the next adjacent element in said one state engages said escapement member;

character escapement selection apparatus for actuating said element setting assembly and said means to remove in the order stated to allow movement of elements in said path and corresponding movement of said carrier equal to a number of said elements associated witha selected character;

means to move said elements in a direction opposite to 23 the direction in which said elements are moved by said drive means;

backspace keylever means controlling the actuation of said means to move;

an element sensing means for sensing the presence of one of said elements in said one state when said elements are moving in said opposite direction; and

means responsive to said element sensing means for deenergizing said means to move when said element sensing means senses an element in said one state to permit backspacing in accordance with the past esoapement informaion represented by said elements.

5. Escapement apparatus for use in a typewriter comprising:

a typewriter frame and a typewriter carrier;

a driven member supported in said frame and having a driving connection with said carrier to control movement of said carrier with respect to said frame;

drive means for driving said driven member in one direction comprising a plurality of elements movable in a path;

each of said elements being settable to at least two states;

an element setting assembly located adjacent said path for setting and maintaining the elements adjacent said element setting assembly in selected states;

an escapement assembly comprising ,a movable escapement member engaging those of said elements in one of said states;

means to remove said escapement member from engagement with one of said elements in said one state to permit movement of said elements in said path and said driven member until the next adjacent element in said one state engages said escapement member;

character escapement selection apparatus for actuating said element setting assembly and said means to remove in the order stated to allow movement of elements in said path and corresponding movement of said carrier equal to a number of said elements associated with a selected character;

said escapement assembly comprises a holding member mounted for movement in adjacent side-by-side rela tion with respect to said escapement member;

said holding member being adapted to engage each of said elements regardless of the states thereof to prevent movement of said elements by said drive means; and

said means to remove comprises means to move and hold said holding member out of engagement with said elements until said escapement member is returned to its initial condition by the next adjacent element in said one state.

6. Escapement apparatus for use in a typewriter comprising:

a typewriter frame and a typewriter carrier;

a driven member supported in said frame and having a driving connection with said carrier to control movement of said carrier with respect to said frame;

drive means for driving said driven member in one direction comprising a plurality of elements movable .in a path;

each of said elements being settable to at least two states;

an element setting assembly located adjacent said path for setting and maintaining the elements adjacent said element setting assembly in selected states;

an escapement assembly comprising a movable escapement member engaging those of said elements in one of said states;

means to remove said escapement member from engagement with one of said elements in said one state to permit movement of said elements in said path and said driven member until the next adjacent element in said one state engages said escapement member;

24-- character escapement selection apparatus for actuating said element setting assembly and said means to remove in the order stated to allow movement of elements in said path and corresponding movement of said carrier equal to a number of said elements associated with a selected character; said element setting assembly comprises a pair of element setting arms positioned on opposite sides of said path;

each of said arms having spaced upper and lower portions joined by an intermediate portion; means mounting said element setting arms in a toggletype linkage system which is operative to move said intermediate portions toward said elements; and

element setting projections on said intermediate portions of said arms adapted to engage at least a portion of the elements positioned between said element setting arms.

7. Apparatus according to claim 6 further characterized by:

at least one element setting mechanism comprising a pair of element setting interposers each having an element setting projection thereon disposed on opposite sides of said path; said element setting interposers being movable toward said elements by said element setting arms; and

means to shift said interposers to selectively position one of said element setting projections on said interposers in aligned element engaging relation with respect to an element.

8. Escapement apparatus for use in a typewriter comprising:

a typewriter carrier and means to move said typewriter carrier;

said means to move comprising a plurality of elements;

means tending to move said elements in a path in a first direction;

each of said elements being settable to at least two states;

an element setting assembly located adjacent said path for setting and maintaining said elements adjacent said element setting assembly in selected states;

an escapement assembly for engaging at least those of said elements in one of said states to limit movement of said elements in said path in said first direction;

a retractable sensing means mounted adjacent said path and adjacent said escapement assembly movable from a retracted position out of said path to an extended position into the path of travel of said elements in one of said states and from said extended position to said retracted position;

actuating means;

driving means for moving said elements in said path in a second direction;

means interconnecting said actuating means, said drive means and said sensing means for actuating said drive means to move said elements in said path in said second direction when said actuating means is operated; and

said sensing means being operative to de-energize said drive means and move from said extended position to said retracted position when one of said elements in said one state is sensed by said sensing means after operation of said actuating means.

9. Backspacing apparatus for use in a typewriter having escapement mechanism for controlling the backspacing movement of a typewriter carrier comprising:

a plurality of spaced elements movable in a path of travel drivingly coupled to said carrier;

means biasing said spaced elements for movement in said path of travel in one direction corresponding to movement of said carrier in the forward escapement direction;

a sensing member located adjacent the path of travel of said elements;

means mounting said sensing member for movement from a retracted position out of said path of travel of said elements to an extended position into said path of travel of said elements and from said extended position to said retracted position;

keylever means; 4

drive means for moving said elements in said path of travel in the opposite direction corresponding to movement of said carrier in the backspacing direction;

means interconnecting said keylever means, said drive means and said sensing member for moving said sensing member from said retracted position out of said path of travel of said elements to said extended position in said path of travel of said elements and actuating said drive means to move said elements in said path of travel and said carrier in the backspacing direction when said keylever means is actuated; and

said interconnecting means being operated by said sensing member to de-energize said drive means when said sensing member is moved from said extended to said retracted position.

10. Backspacing apparatus for use in a typewriter having escapement mechanism for controlling the backspacing movement of 'a typewriter carrier comprising:

a plurality of spaced elements movable in a path of travel drivingly coupled to said carrier;

means biasing said spaced elements for movement in said path of travel in one direction corresponding to movement of said carrier in the forward escapement direction;

a sensing means locatedadjacent the path of travel of said elements;

means mounting said sensing means for movement from a retracted position out of said path of travel of said elements to an extended position into said path of travel of said elements and from said extended position to said retracted position;

actuating means;

drive means'for moving said elements in said path of travel in the opposite direction corresponding to movement of said carrier in the backspacing direction and for moving said carrier in the backspacing direction; f

means interconnecting said actuating means, said drive means and said sensing means for moving said sensing means from said retracted position out of said path of travel of said elements to said extended position in said path of travel of said elements and actuating said drive means to move said elements in said path of travel and said carrier in the backspacing direction when said actuating means is actuated; and

said interconnecting means being operated by said sensing means to de-energize said drive means when said sensing means is moved from said extended to said retracted position.

11. Proportional escapement apparatus for use in a typewriter comprising:

a typewriter frame and a typewriter carrier;

means mounting said frame and said carrier for relative movement in both longitudinal directions;

means for controlling the extent of said relative movement in both directions comprising a memory device;

said memory device having a plurality of elements each settable to at least two states;

sensing means comprising at least one sensing assembly responsive to those of said elements which are in one of said states;

character selection apparatus; 7

means for determining the states of said elements in accordance with the actuation of said character selection apparatus to store escapement information in said memory device corresponding to and in proportion to the widths of selected characters with the number of elements in a first state between adjacent elements in a second state determining the escapement movement associated with a selected character;

said memory device retaining and storing the escapement information corresponding to previously selected characters; and

means for eifecting relative movement in both directions between said settable elements and said sensing means until said sensing means senses the next adjacent element in said second state in the direction of relative movement between said settable elements and said sensing means to permit said relative movement of said frame and said carrier on a characterby-character basis in both directions.

12. Apparatus according to claim 11 further characterized by:

said settable elements being arranged in series relation with respect to each other and in a closed path to define a continuous memory for said escapement information corresponding to previously selected characters;

said means for determining operating at the same time on a plurality of said settable elements correspondingly to the largest number of settable elements associated with any of said selected characters; and

said means for determining being operative to insure the element in said plurality of elements located furthest from said sensing means in one direction of relative movement between said settable elementsand said sensing means is always in said one of said states.

13. Proportional escapement apparatus for use in a typewriter comprising:

a typewriter frame and a typewriter carrier;

means mounting said frame and said carrier for relative movement in both longitudinal directions;

means for controlling the extent of relative movement in both directions comprising a memory device;

means to move said memory device in one direction;

said memory device having a plurality of elements each settable to at least two states;

sensing means comprising an actuatable escapement assembly responsive to those of said elements which are in one of said states to permit movement of said memory device in one direction;

character selection apparatus;

means for determining the states of said elements in accordance with the activation of said character selection apparatus to store escapement information in said memory device corresponding to and in proportion to the widths of selected characters with the number of elements in a firststate determining the escapement movement associated with -a selected character;

said memory device retaining and storing the escapement information corresponding to previously selected characters; I

backspacing means for moving said memory device in the opposite direction without altering the proportional escapement information stored in said memory' device to cause movement of said carrier from one printing position to another previous printing position; and

forwardspacing means for actuating said escapementasssembly and inhibiting the operation of said means for determining to cause said carrier to return to said one printing position from said another and previous printing position on a character-by-character basis.

14. Escapement apparatus for use in a typewriter comprising:

a plurality of elements arranged in a closed path;

each of said elements being settable to at least two states; character selection apparatus; means for determining the states of said elements in accordance with the actuation of said character selection apparatus; said means for determining comprising a pair of element setting arms positioned on opposite sides of said path; each of said arms having spaced upper and lower portions joined by an intermediate portion; means mounting said element setting arms in a toggletype linkage system which is operative to move said intermediate positions toward said elements; and element setting projections on said intermediate portions of said arms adapted to engage at least a portion of the elements positioned between said element setting arms. 15. Apparatus according to claim 14 characterized by: at least one element setting mechanism comprising a pair of element setting interposers each having an element setting projection thereon disposed on opposite sides of said path; said element setting interposers being movable toward said elements by said element setting arms; and means to shift said element setting interposers to selectively position one of said element setting projections on said element setting interposers in aligned element engaging relation with respect to an element. 16. Apparatus according to claim 15 further characterized by:

means to latch said element setting interposers in at least one shifted state. 17. Apparatus according to claim 16 further 'charac terized by:

said means to latch comprises a notch in one of said element setting interposers adapted to engage and latch against the adjacent element setting arm; and means to release said means to latch. 18. Escapement apparatus for use in a typewriter comprising:

a plurality of elements arranged to move in a path; each of said elements being settable to at least two states; character selection apparatus; means for determining the states of said elements in accordance with the actuation of said character selection apparatus; said means for determining comprising pairs of ele ment setting members with the setting members of each pair positioned on opposite sides of said path; each of said members carrying an element setting projection;

means mounting said element setting members of eachpair for inward movement toward each other and said path;

means to move said pairs of element setting members to cause at least a portion of said element setting projections to engage the elements positioned adjacent said means for determining;

an escapement assembly comprising an escapement member adapted to engage those of said elements in one of said states; and

means to remove said escapement member from engagement with those of said elements in said one state to permit movement of said elements in said path until the next adjacent element in said one state engages said escapement member.

19. Apparatus according to claim 18 further characterized by:

means to actuate said means to move and said means to remove in the order named in response to operation of said character selection apparatus; and

28 said means to actuate comprises a pair of cam and cam follower assemblies. 20. Apparatus according to claim 18 further characterized by:

said escapement assembly comprises a holding member mounted for movement in adjacent side-by-side relation with respect to said escapement member;

said holding member being adapted to engage each of said elements regardless of the states thereof to prevent movement of said elements in said path; and

said means to remove comprises means to move said holding member out of engagement with said ele ments prior to disengagement of said escapement member and to maintain said holding member out of engagement until said escapement member is returned to its initial condition by said next adjacent element in said one state.

21. Escapement apparatus for use in a typewriter comprising:

a plurality of elements movable in a path of travel;

each of said elements being settable to at least two states;

an escapement assembly for preventing movement of said elements in said path;

said escapement assembly comprising an escapement pawl mounted for pivotal and limited longitudinal movement;

said escapement pawl having a tip portion;

means biasing said tip position of said escapement pawl into engagement with said settable elements which are in One of said states;

a holding pawl mounted for pivotal movement in adjacent side-by-side relation with respect to said escapement pawl;

said holding pawl having a tip portion;

means biasing said tip portion of said holding pawl into engagement with said elements regardless of the states thereof;

means to remove said escapement and holding pawls from engagement with said elements;

said means to remove comprising means to pivot said escapement and holding pawls against the action of said biasing means; and

means to hold said tip portion of said holding pawl out of engagement with said elements until said escapement pawl has been engaged by an element in said one state and returned to its initial condition.

22. Apparatus according to claim 21 further characterized by:

said means to hold comprises a latch means formed by projecting portions of said escapement and holding pawls.

23. Apparatus according to claim 21 further characterized by:

each of said escapement and holding pawls has a rear end portion;

said means to remove comprising a pawl release lever mounted for pivotal movement and having a portion overlying the rear end portions of said escapement and holding pawls;

said rear end portion of said holding pawl projecting to one side of said rear end portion of said escapement pawl;

means to pivot said release lever; and

said projection on said release lever engaging said rear end portion of said holding pawl to pivot said tip portion of said holding pawl out of engagement with said elements prior to pivoting said escapement pawl out of engagement with said elements in said one 70 state.

24. Apparatus according to claim 23 further characterized by:

said means to hold comprises a projection on said hollding pawl and a tab on said escapement pawl; an 

1. ESCAPEMENT APPARATUS FOR USE IN TYPEWRITER COMPRISING: A TYPEWRITER FRAME AND ATYPEWRITER CARRIER; A SINGLE PRINT ELEMENT HAVING CHARACTERISTICS THEREON REMOVABLY MOUNTED ON SAID CARRIER; CHARACTER SELECTION MEANS FOR MOVING SAID PRINT ELEMENT TO BRING A SELECTED CHARACTER INTO PRINTING POSITION; MEANS TO ROCK SAID PRINT ELEMENT TO MOVE SAID PRINT ELEMENT IN A DIRECTION TO EFFECT PRINTING OF A CHARACTER IN SAID PRINTING POSITION; AN ELONGAED LEAD SCREW SUPPORTED IN SAID FRAME AND HAVING A DRIVING CONNECTION WITH SAID CARRIER TO CONTROL MOVEMENT OF SAID CARRIER AND SAID PRINT ELEMENT WITH RESPECT TO SAID FRAME; DRIVE MEANS OPERATIVELY CONNECTED TO AND LOCATED ADJACENT ONE END OF SAID LEAD SCREW TENDING TO ROTATE THE SAME IN ONE DIRECTION; A GENERALLY CIRCULAR DISC SHAPED PIN WHEEL CARRYING A PLURALITY OF PINS LOCATED ADJACENT THE OTHER END OF SAID LEAD SCREW; A PLURALITY OF SELECTABLE GEAR MEANS EACH OPERATIVE WHEN SELECTED TO DRIVINGLY INTERCONNECT SAID LEAD SCREW AND SAID PIN WHEEL; EACH OF SAID PINS BEING MOVABLE TO AT LEAST TWO POSITIONS DEFINING AT LEAST TWO STATES AND THE DISTANCE BETWEEN ADJACENT PINS DEFINING A BASIC ESCAPEMENT UNIT; A PLURALITY OF CHARACTER KEYLEVERS EACH ASSOCIATED WITH AT LEAST ONE OF THE CHARACTERS TO BE PRINTED; A PIN SETTING ASSEMBLY LOCATED ADJACENT SAID PIN WHEEL FOR MOVING AND MAINTAINING THE PINS ADJACENT SAID PIN SETTING ASSEMBLY IN SELECTED STATES; AN ESCAPEMENT ASSEMBLY COMPRISING AN ESCAPEMENT PAWL MOUNTED FOR PIVOTAL AND LIMITED LONGITUDINAL MOVEMENT FOR ENGAGING THOSE OF SAID PINS IN ONE OF SAID STATES TO HOLD SAID PIN WHEEL AGAINST ROTATION BY SAID DRIVE MEANS; 